Formula
A rectangle is length × width × average depth. A round pool uses the length as the diameter: π × radius² × depth. An oval is an ellipse, π × (length / 2) × (width / 2) × depth. A kidney or other freeform pool is the bounding rectangle times a factor that starts at 0.85. Average depth is the shallow end plus the deep end, divided by two, which is exact for a straight slope and only a sketch for a hopper.
gallons = cubic feet × 7.48052
litres = cubic feet × 28.3168
One US gallon is 231 cubic inches, and 7.48052 gallons fit in a cubic foot. The pool salt calculator multiplies these gallons by the ppm gap. It does not tell you how to mix the salt.
Worked examples
32 × 16 ft, 5 ft average depth. 2,560 ft³. 2,560 × 7.48052 = 19,150 gallons.
The same pool, 3 ft to 8 ft. Average depth is 5.5 ft, so the volume is 10% more than the flat 5 ft pool.
A 24 ft round pool, 4 ft deep. π × 12² × 4 cubic feet, then the same 7.48052.
Reference
The freeform factor is the only number that is not geometry. Change it.
| Shape | Water volume |
|---|---|
| Rectangle | L × W × depth |
| Round | π × (diameter / 2)² × depth |
| Oval | π × (L / 2) × (W / 2) × depth |
| Kidney / freeform | L × W × 0.85 × depth |
Questions
How do I handle a beach entry or a hopper?
Average the shallow depth and the deep depth, which is what a constant slope does. A hopper that is only part of the floor is not that average. Measure it in pieces, or treat the freeform factor as the fudge, and say so.
What is the kidney factor?
Length times width times 0.85 times depth. It is a bounding-box approximation, not a survey. Change 0.85 if you have a better sketch of the waterline.
Does this include the plumbing?
No. This is the water in the pool. Salt for that gallon count is the pool salt calculator. Pipe volume is a different tool.
Sources
- 1 cubic foot = 7.48052 US gallons. 1 cubic foot = 28.316846592 litres, from 0.3048³ × 1,000.
- The 0.85 kidney factor is a planning approximation for this page. A measured waterline replaces it.